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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

    <strong>11</strong>
    <div>
        <h1></h1>
        <h3></h3>
        <h4>1</h4>
        <h4>1</h4>

    </div>

</body>
<script src="js/jquery.min.js"></script>
<script>
    $(() => {
        //兄弟节点下的下标
        //所以是从h1 h3 h4开始下标为1;
        console.log($('h3').index());
        //eq()选择同一个标签的下标
        $('h4').eq(0).html('111');
    });
</script>

</html>